PyUSB send HID report

Question

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UPDATE

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I managed it to send the data properly. For anyone how ran into the same problem, I used the following code:

data=[0x00, 0x04, 0x04, 0xFF, 0xFF, 0xFF, 0x00, 0x00]
result=dev.ctrl_transfer(0x21, 0x9, wValue=0x200, wIndex=0x00, data_or_wLength=data)

(this is based on the answer posted here: link )

But I don't understand in detail, why I have to use

bmRequestType=0x21
bRequest=0x9
wValue=0x200

If anyone could explain it in more detail, I would be grateful. I just want to learn.

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Initial request:

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I'm desperately trying to send a simple report to a HID-device using PyUSB.

Using "SimpleHIDwrite" I confirmed, that the device works just as expected. I want to send this data:

report ID: 00

data: [00, 04, 04, FF, FF, FF, 00, 00]

sending data using SimpleHIDwrite

I'm quite new to python and USB and I can't figure out how to do this using dev.ctrl_transfer or dev.write.

Also, there are some posts about sending data to HID devices, but I couldn't figure out how to solve my problem.

Could anybody please be so kind to point me in the right direction?

Thank you very much!

Here are some more details:

 # based on https://github.com/walac/pyusb/blob/master/docs/tutorial.rst

import usb.core
import usb.util

# find our device
# dev = usb.core.find(idVendor=0xfffe, idProduct=0x0001)
dev = usb.core.find(idVendor=0x1781, idProduct=0x8c0)


# was it found?
if dev is None:
    raise ValueError('Device not found')

dev.set_configuration()

cfg=dev[0]
intf=cfg[(0,0)]
ep=intf[0]

# dev.write(ep.bEndpointAddress, [0x00, 0x00,0x04,0x04,0xFF,0xFF,0xFF,0x00, 0x00], 1000)
# dev.ctrl_transfer(bmRequestType, bRequest, wValue=0, wIndex=0, data_or_wLength=None, timeout=None)

print("print ep")
print(ep)
print("print cfg")
print(cfg)
print("print intf")
print(intf)

And the result of the script above is this:

print ep
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa
print cfg
  CONFIGURATION 1: 100 mA ==================================
   bLength              :    0x9 (9 bytes)
   bDescriptorType      :    0x2 Configuration
   wTotalLength         :   0x22 (34 bytes)
   bNumInterfaces       :    0x1
   bConfigurationValue  :    0x1
   iConfiguration       :    0x0 
   bmAttributes         :   0x80 Bus Powered
   bMaxPower            :   0x32 (100 mA)
    INTERFACE 0: Human Interface Device ====================
     bLength            :    0x9 (9 bytes)
     bDescriptorType    :    0x4 Interface
     bInterfaceNumber   :    0x0
     bAlternateSetting  :    0x0
     bNumEndpoints      :    0x1
     bInterfaceClass    :    0x3 Human Interface Device
     bInterfaceSubClass :    0x0
     bInterfaceProtocol :    0x0
     iInterface         :    0x0 
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa
print intf
    INTERFACE 0: Human Interface Device ====================
     bLength            :    0x9 (9 bytes)
     bDescriptorType    :    0x4 Interface
     bInterfaceNumber   :    0x0
     bAlternateSetting  :    0x0
     bNumEndpoints      :    0x1
     bInterfaceClass    :    0x3 Human Interface Device
     bInterfaceSubClass :    0x0
     bInterfaceProtocol :    0x0
     iInterface         :    0x0 
      ENDPOINT 0x81: Interrupt IN ==========================
       bLength          :    0x7 (7 bytes)
       bDescriptorType  :    0x5 Endpoint
       bEndpointAddress :   0x81 IN
       bmAttributes     :    0x3 Interrupt
       wMaxPacketSize   :    0x8 (8 bytes)
       bInterval        :    0xa

Process finished with exit code 0

Answer 1

Don't use PyUSB (unless you need other protocols too). Managing HID isn't difficult, but there is a much easier solution.

HIDAPI is a C-library which manages the protocol, and there is a Python wrapper available too.

Also, it hides the necessity to take control back from the operating system, which recognizes the HID protocol on connection, and install its own driver.

Answer 2

This is all you need to do HID with PyUSB:

  def hid_set_report(dev, report):
      """ Implements HID SetReport via USB control transfer """
      dev.ctrl_transfer(
          0x21, # REQUEST_TYPE_CLASS | RECIPIENT_INTERFACE | ENDPOINT_OUT
          9, # SET_REPORT
          0x200, 0x00,
          report)

  def hid_get_report(dev):
      """ Implements HID GetReport via USB control transfer """
      return dev.ctrl_transfer(
          0xA1, # REQUEST_TYPE_CLASS | RECIPIENT_INTERFACE | ENDPOINT_IN
          1, # GET_REPORT
          0x200, 0x00,
          64)

No need to jump onto the library-wrappers-around-libraries bandwagon. Are you an engineer or what? Just read the doc. The protocol is not going to change anytime soon.

Finally, yeah. All the 4 libusbhid's I've seen are written in disastrously horrible C and depend on yet even more libraries. For what is essentially 10 lines of code. Make your own decision.